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AN ARTICLE 

ON THE 

AGENCY OF THE GULF STREAM 

IN THE FORMATION OF 

THE PENINSULAR AND pYS OF FLORIDA. 
BY JOSEPH LeCONTE, M. D. ; 

PItOFESSOU OF CHEMISTRY, MINERALOGY AND GEOLOGY, IN THE SOUTH CAROLINA COLLEGE. 

Head before tho American Association for the advancement of Scionco at Albany, 

August, 1S5-1. 



In the winter of 1851, and during the months of January and Feb- 
ruary, I enjoyed the rare opportunity of visiting and examining the 
keys and reefs of Florida, in company with Professor Agassiz. I then 
and there became deeply interested in a subject which has continued to 
occupy my thoughts from time to time until now — viz. : the mode of 
formation of the peninsula of Florida. 

Until the time referred to, nothing definite was known of the geology 
of Florida, but it was supposed to consist of a southward prolongation 
of the eocene of Georgia and Alabama, and its shell limestone to bear 
some general resemblance to the white limestone of these States. But 
the observations of Professor Tuomey during the summer of 1850,* and 
the more full and careful observations of Professor Agassiz during the 
following winter, j - brought to light the remarkable fact that the keys 
and the larger portion of the peninsula of Florida are of recent origin, 
and as far as could be examined the work of corals still living in the 
vicinity, and still engaged in the work of extention ; that they are, 
in fact, superficially at least, the result of the growth of successive coral 
reefs, concentrically arranged, one outside of the other, from north to 
south. My object in the present paper will be to show that coral 
agency alone is not sufficient to account for the phenomena, but that 
there has been another and still more powerful agent at work, preparing 
the ground and laying the foundation for these builders, and that this 
agent has been the Gulf Stream. A clear understanding of the subject 
•renders necessary a succinct account of the views of Tuomey and 
Agassiz. 

* Am. Jour. Sci. and Arts, vol. i., p. 390. f Report of Coast Survey for 1851, p. 145. 



&*. 






Fig. 1 represents the peQinaula of Florida with its keys and reefs ; a 5> the south- 
ern coast; a' b' the line of keys stretching from Cape Florida to the Tortugas; a" b' 1 
the living reef; G S S the Gulf Stream sweeping close around the reef; d, Tampa Bay ; 
d', Charlotte's Harbor; d", Chatham, or Gallivari Bay. 

The southern coast a b is elevated about 12—15 feet above the level 
of the sea ; but within this line there is e, the everglades, an extensive 
swamp only a few feet above the sea level, covered with fresh water, 
and dotted over with small islands called Hammocks. Between the 
southern coast a b and the line of keys d b' — a distance at the point b of 
about 40 miles — the water is very shoal, navigable only for the smallest 
fishing craft, and dotted over with small low mangrove-islands. 



Between the line of the keys a' b' and the living reef a" b", there is a 
ship channel 3 or 4 fathoms deep and 5 or 6 miles wide. Beyond the 
reef a" b" the sea bottom slopes rapidly into the almost unfathomablo 
abyss of the Gulf Stream. 

Now, we have the best evidence that the everglades, the southern 
coast and the keys, are all formed by coral agency. The evidence is 
briefly as follows : 

It is well known that the corals cannot grow above the surface of 
the water. The islands, therefore, so commonly found on coral reefs, 
cannot be formed by the agency of these animals alone, but arc due to 
the violent action of waves breaking off huge coral heads and over- 
turning coral trees, bearing them from the outer and more exposed side, 
aud piling them on the middle and inner side of the reef. These coral 
boulders form the nucleus around which cluster smaller fragments and 
coral sand; the whole is then firmly cemented by carbonate of lime in 
solution in the sea water, and the island thus formed is finally covered 
with vegetation, and inhabited by animals and man. The whole em- 
bryonic development, if I might use the expression, of coral islands, 
may be observed upon the keys and reefs of Florida. On the outer or 
living reef, a few have commeuced to form, only a few years ago, and 
exist as yet only in the form of isolated boulders of dead coral, and 
not yet dignified with the name of keys. Others are formed of similar 
boulders, mingled with smaller fragments and coral sand, and firmly 
cemented by carbonate of lime; but the large boulders are still con- 
spicuous above the surrouuding land, though immovably fixed. Still, 
others are so covered with coral sand that the buulders are not observ- 
able, except by excavation, or by examination of the outermost portion 
of the island towards the sea. The coral sand is always affected with 
the cross aud oblique stratification, so common in materials exposed to 
the violent actions of the waves. All the islands on the outer reef are 
very small, of very recent origin, (some only a few years old,) and 
therefore, as yet, entirely barren. 

The examination of the larger and older inhabited islands of the line 
of keys prove, beyond question, that they have been formed in a similar 
manner. We have here, also, the same coral boulders, mingled with 
smaller fragments and coral sand, and the whole firmly cemented into 
solid rock, the same cross and oblique stratification indicating the former 
action of waves on an exposed shore. The boulders here, also, sometimes 
stand above the surrounding cement, exposed in their superior portions, 
as at Key Vacca ; and at others completely covered with coral sand, as at 
Key West, aud most other keys. This exposure of the larger boulders 
above the surrounding cement in which they are firmly fixed, led 
Tuomey into the error of supposing that they were the prominent points 
of the original reef, elevated above the sea level by igneous agency, 
and that the keys were formed by igneous, rather than by aqueous 
agency. That such is not the case, is proved by more attentive exami- 
nation and comparison with the smaller keys of the outer reef. There 
can be no doubt, therefore, that the line a' V , marks the position of a 
former reef, changed into keys by the action of waves alone. 



It has been pointed out by Tuomey, and proved by Agassiz, that in 
a similar manner, the southern coast of Florida was the position of still 
another and earlier reef. The character of the rock is the same as 
that of the keys of the main range, or of the smaller ones on the living 
reef. Here, also, Tuomey has seen, as he supposes, the evidence of 
elevatory forces, while Agassiz sees nothing but the action of the 
waves. 

There seems to be no reasonable doubt, therefore, that at some former 
period, the northern shore of the everglades was the position of the 
southern coast, and at the same time, the present southern coast was the 
position of a reef. The general sequence of changes has been as fol- 
lows : The reef a b became gradually converted into a line of keys, 
and was finally added to the main land, and the shoal water became the 
everglades, and its mangrove islands, the hammocks which overdot this 
swamp. In the meantime, that is, while the present southern coast 
was still a line of keys, another reef was formed farther out. This 
became in time, converted into a line of keys, and will eventually be 
added, in its turn, to the main land, and become the southern coast — 
the shoal water between a b and a' b', with its mangrove islands, be- 
coming another everglade, with its hammocks. In the meantime, still 
another reef has been formed still farther out, (viz : the present or 
living reef,) and upon this, too, the process of key formation has 
already commenced. Any further extension, however, in this direction, 
by the growth of still another reef, seems precluded by the proximity 
of deep water. Standing upon the reef, the blue waters of the Grulf 
Stream are distinctly seen at the distance of but a few hundred yards. 
Thus it appears, that not only the keys, but the mainland of Florida, 
certainly as far north as the northern shores of the everglades, has been 
formed superficially, at least, by coral agency. The evidence in favor 
of a similar origin for that portion of the peninsula lying north of this 
line, is less abundant, and perhaps less conclusive, and yet we have 
every reason to believe that the greater portion of this, also, was formed 
in a similar manner. Although the geology of this part has not, as far 
as I know, been examined by any one capable of deciding definitely as 
to what portion of the peninsula is tertiary, and what is recent coral 
formation, yet specimens of coral rock, precisely similar to that of the 
southern coast and keys, sent to Professor Agassiz from the shores of 
Lake George, and other parts of Florida, as far north as St. Augustine, 
leave no doubt, that on the eastern coast, at least, the coral formation 
extends as far north as that ancient city. I have, myself, a fragment 
of Meandrina, from the neighborhood of St. Augustine, undistin- 
guishablc from fragments which may be picked up anywhere upon the 
keys. "The western shore is still less known ; but Conrad and Tuomey 
state it as their opinion, that the bluffs of Tampa are eocene tertiary. 
Supposing this to be a fact, though it is still problematical, then all that 
portion of the peninsula lying south of the lin3 c d is almost certainly 
of coral origin, and formed in the manner already indicated, viz : by 
the growth of successive reefs. As to the position of those supposed 
reefs, we know absolutely nothing. The position of the lines c d, c' d', 



c" d" has been merely suggested by the succession of bays which indent 
the western coast. May they not all have been formed like Chatham 
bay, by the imperfect filling up of the shoal water, separating succes- 
sive reefs from the mainland ? 

Such is a brief account of Professor Agassiz's views concerning the 
mode of formation of the peninsula and keys of Florida. I will now 
attempt to show, that coral agency alone, is not sufficient for this pur- 
pose, and that to suppose so, would violate all probability, and contra- 
dict all that we know of the laws which govern the growth of these 
animals. 

It is a well known fact, that reef-building corals cannot grow at a greater 
depth than from ten to twelve fathoms. It is also certain, that they 
cannot grow above the surface of the water at low tide. Thus they 
are limited in a vertical direction to a space of about sixty or seventy 
feet. Unless there is subsidence of the sea bottom, therefore, it is im- 
possible that a reef should be more than sixty or seventy feet thick. To 
this may be added, in the case of coral islands, from ten to fifteen feet, 
for material accumulated above the sea level by the agency of wav^s. 
If there is no subsidence, therefore no coral formation can be more 
than eighty feet in thickness. Now, nothing can be more certain, than 
that there has been no subsidence whatever of the sea bottom, upon 
which grow the reefs of Florida, for otherwise, the extension of the 
peninsula by means of coral agency, would have been impossible. It 
necessarily follows, therefore, that the coral formation of Florida, 
whether upon the maiu land, or upoa the keys, or upon the living reef, 
can nowhere be more than seventy or eighty feet thick. In other 
words, it is evident that Florida and the keys are only faced or encrusted 
with coral formation. If, then, corals have been the only agents in 
this work, if the sea bottom has remained substantially unchanged dur- 
ing the whole time the coral work was progressing, it is evident that 
the sea, for the enormous distance of five degrees of latitude, viz : from 
St. Augustine to the present reef, was nowhere more than sixty or seventy 
feet in depth, and Florida must have been represented by a tongue 
of shoal water three hundred miles in length — a circumstance possible, 
certainly, but so improbable, that it behoves those who maintain the 
theory, that coral alone has formed the peninsula, to account for it. 

But even if we admit the probability of such a condition of things, 
we do not get rid of the main difficulty; for in that case, there is no 
apparent reason why the coral should not grow over the whole area at 
one time, as an immense coral forest, instead of in the form of succes- 
sive reefs. In a word, the fact that the corals grew in the form of suc- 
cessive reefs, concentrically disposed from north to south, proves, as it 
seems to me, incontestibly, that the conditions necessary for coral 
growth have also been progressively formed in the same direction. The 
horizontal extension of coral through so great a space, proves also, the 
progressive extension of necessary conditions ; in other words, it proves 
that the sea bottom has been gradually rising from the north towards 
the south. 

Such a gradual rising of the sea bottom may be attributed to one of 



6 

two causes, viz : first, gradual elevation by igneous agency, and second, 
filling up by sedimentary deposit. As we have already seen, Professor 
Tuomey has thought that they are evidences of such igneous elevation 
upou the keys, as upon the main land ; but the more careful observa- 
tions of Professor Agassiz, have satisfactorily explained these deceptive 
appearances, so that we may now say with confidence, that there is not 
the slightest evidence of such elevation, but much evidence to the con- 
trary. Neither the main land nor the keys are anywhere higher than 
may be accounted for by the action of the waves, viz : from ten to fif- 
teen feet ; and it is inconceivable, that this elevation should have gone 
on progressively preparing ground for the growth of successive reefs, 
without in the slightest degree affecting the contiguous and recently 
formed land. But this is precisely the mode of action of sedimentary 
deposit. Sediment cannot, of course, affect anything but the sea bot- 
tom. It is to sedimentary deposit, therefore, that I attribute the 
gradual rising of the sea bottom from north towards the south, which, as 
we have seen, forms the necessary condition for the horizontal exten- 
sion of coral reefs through so great a distance. 

Having thus shown that sedimentary deposit is almost absolutely 
necessary for the explanation of the southward extension of the reefs 
of Florida, let us attempt to prove that such deposit has, in fact, taken 
place under the influence of the Gulf Stream. 

It is a well known law of currents bearing sediment, that if from any 
cause their velocity is checked, they deposit a portion of their sedi- 
ment upon the bottom ; but if, on (the contrary, their velocity is in- 
creased, they abrade their beds and banks. If, therefore, the velocity 
of a stream is greater on one side than on the other, abrasion will take 
place on the former, and deposit on the latter. Now, if such a stream 
bearing sediment, make a sweep or curve, the velocity will always be 
greater on the outer, and least on the inner side of the sweep. Hence 
there must necessarily be abrasion of the outer bank, and deposit upon 
the inner. Thus, in proportion as the outer curve extends by abrasion 
of the outer bank, the inner curve will extend also by deposit, and the 
tongue of land around which the sweep is made, will grow longer and 
longer. If this tongue is cut away by artificial means, so as to convert 
this portion of the stream into a lake, around the outer margin of which 
sweeps the current, the still water within the sweep will become more 
and more shoal, until it is again converted into a tongue of land. Now, 
this is necessarily true under all cii'cumstances. It makes no difference 
whether the stream runs between banks of solid matter, or between 
banks of still water. If a stream, teaying sediment, runs through 
still water, making a sweep or curve, the sediment must deposit prin- 
cipally upon the inner side of the curve, making shoal water at this 
part — the curve will extend, and the shoal water will extend in the 
same proportion. 

Now, the Gulf Stream is such a current. The sweep which it makes 
around the point of Florida, is seen in fig. 1. If, therefore, the Gulf 
Stream bears any sediment, the conclusion seems irresistable, that the 
sweep of the curve has been increasing with the course of time, and 



that the tongue of land within the curve, viz : the Peninsula of Flori- 
da, has been extending, pari posSU, by means of sedimentary deposit. 
Or, even supposing that the position of tbe Gulf Stream has alwaj's 
been the same as at present, and that Florida was once represented by a 
tongue of still water within the curve, this tongue of still water must 
have become more and more shoal by sedimentary deposit. I repeat, 
then, that upon any conceivable theory as to the position of the Gulf 
Stream, whether its curve has been increasing, or has been always the 
same as at present, if it carries sediment according to the laws of cur- 
rents, there must have been a progressive shoaling of water within the 
curve from north toward tbe south, and, consequently, a progressive 
formation of the conditions necessary to the growth of coral, and their 
extension in the same direction. What evidence, then, have we that 
the Gulf Stream does indeed carry sediment? 

The Gulf Stream is supposed to be a continuation of the great equa- 
torial current, which, stretching across the Atlantic from the coast of 
Africa, strikes upon the wedge-shaped point of the eastern coast of 
South America, and divides into a northern and southern branch. The 
northern branch, uniting with the water of the Amazon and Orinoco, 
runs along the coast of South America, through the Carribean Sea, 
under the name of the Carribean current, enters and receives strength 
in the Gulf of Mexico, from which, emerging, it sweeps round the 
point of Florida, and along the coast of the United States, on its way to 
the coast of Europe. 

Now, is it possible, that a stream which washes so many shores, which 
runs through seas into which are poured such enormous quantities of 
sediment, brought down by the largest rivers in the world, is it conceiv- 
able that such a stream should carry no sediment ? On the contrary, it 
is well known that the sediment, both of the Amazon and Orinoco rivers, 
is carried by this stream, and is distinctly traceable for several hundred 
miles. Much of it is doubtless deposited along the coast and in the 
Carribean Sea, but " according to Humboldt, much sediment is carried 
again out of the Carribean Sea into the Gulf of Mexico."* Into this 
same Gulf is also poured the enormous amount of sediment brought 
down by the Gulf rivers, especially by the Mississippi. Out of this 
Gulf, the waters of which are thus highly charged with sediment, 
comes the Gulf Stream on its way round the point of Florida. If, then, 
this stream mingles at all with the waters of the Gulf rivers, it must 
necessarily carry sediment. That it does thus mingle, is proved by the 
fact mentioned by Lyell,f that drift timber from the Mississippi is carried 
by this stream to the shores of Iceland and Europe. Now unless we 
suppose that the whole of this sediment is deposited in the Gulf, it must 
reach, and, by the law of currents, already insisted on, be deposited, 
much of it, on the point of Florida. But we have the best reason for 
believing that it is not all deposited in the Gulf. The distance from 
the mouth of the Mississippi to the Tortugas is about five hundred 
miles. Taking the velocity of the Gulf Stream through the Gulf of 

*Lyell's Prin., p. 328. t L y ell ' s Prin -> P- Ml. 



Mexico at three miles per hour, it would traverse this distance in about 
seven days. Now, the finest sediment will not sink more than J an inch 
in an hour; but supposing the mud brought down by the Mississippi 
sinks at the rate of one foot per hour, in seven days it would sink 168 
feet. But the depth of the Gulf of Mexico and the Gulf Stream is 
much greater than this. Therefore, fine sediment from the Mississippi 
would reach the point of Florida, and what was not deposited there 
would even be carried much farther on. We have farther evidence of 
this in the soundings made by the Coast Survey off' the eastern coast of 
Florida, and the nature of the bottom which has thus been brought up. 
It can scarcely be doubted for a moment that the banks of sand and 
mud, found in the bed and on the margin of the Gulf Stream off the 
eastern coast of Florida, were deposited there by that stream. 

But it will be objected that the water of the Gulf Stream is remark- 
able for its transparency. This objection, however, will entirely disap- 
pear, when we consider the difference between the river and ocean cur- 
rents. The former are of slight depth, and run over rough bottoms, 
and between banks possessing many inequalities of surface, and offer- 
ing, therefore, much resistance ; hence are generated partial currents, 
upward and downward, to the right and left, which thoroughly mix, as 
if by a sort of ebulition, the waters of the river. It is impossible that 
matters in suspension or solution should exist in one part and not in 
another ; e. g., that sediment should be carried by the deeper strata, 
while the superficial strata remains transparent. But with oceanic 
streams the case is quite different. Their great depth, and the fact 
that they are bounded on all Sides by still water; in other words, that 
they run over perfectly even beds, and between perfectly smooth banks, 
causes them to flow without the slightest agitation, without the ripples 
and inequalities which mark the currents of rivers. The currents of 
oceanic streams, therefore, do not in the slightest degree interfere with 
the natural subsidence of materials in suspension. They are equally as 
favorable to subsidence as perfectly still water. The surface transpa- 
rency of the Gulf Stream, therefore, forms no objection whatever to the 
supposition that it carries sediment in the deeper strata. Such sedi- 
ment would necessarily sink beyond observation in the course of a few 
hundred miles. 

JLyell's Prin., p. 328. 






^ v 



III (^ 



— t — I — "~" I I ... 




/ 




After what I have said above, the bare inspection of the accompanying- 
figures will explain the application of the theory to the formation of the 
Peninsula and Keys. 



Figs. 2, 3 and 4, are ideal sections through the middle of the Peninsula and Keys, 
along the line p^ fig. 1, representing the different stages of the process; I I the sea 
level, G S the Gulf Stream, c" a a' a" sections of the lines c" d" a b a' b' a" b" of 
fig. 1. Fig. 2 represents the condition of things at some period anterior to the present 
elongation of the Peniasula, e. g., when the southern coast was in the position of the 
northern shores of the everglades, c" n o the supposed configuration of sea bottom 
at that time. At the point n, at the depth of 60 feet would form a reef, a, leaving a 
ship channel e between the coast and reef. Fig. 3 represents the condition of things 
when the sea bottom by sedimentary deposit had advanced to a n' o'. The reef, a, 
has become now a line of Keys, the ship channel e has become shoal water, dotted over 
with mangrove islands, (not here represented,) and another reef, a', has formed at the 
limiting depth of 60 feet, leaving another ship channel e' between the reef and the 
Keys. Fig. 4 represents the condition of things when the sea bottom had advanced to 
a' n" o". Now a, the line of Keys of the last figure, has become the southern coast, 
the former shoal water e has become the everglades, «', the reef of Inst figure, has 
become a line of Keys, and its ship channel e' shoal water, and at the limiting depth 
of 60 feet still another reef a", viz. : the present living reef is formed with its ship 
channel e". This figure, therefore, represents the present condition of things. 
9 



10 

It is evident that if this theory be correct, and no insuperable obstacle 
is interposed, the Gulf Stream may continua to move its bed, and the 
point of Florida to extend almost indefinitely. But such an obstacle is 
interposed in the island of Cuba. The Gulf Stream cannot move much 
beyond its present position, nor Florida extend' beyond the position of 
the present -reef, except at the expense of Cuba and the Bahama Banks. 
Cuba never can be annexed by any natural agency, whether coral or 
current. 

Or even supposing (as I have already done) that the position of the 
Gulf Stream has always been the same as at present, and that the pen- 
insula of Florida was originally represented by a tongue of still water, 
yet, substantially the same changes would necessarily have occurred. 

It is evident, that as the point of Florida approached the Gulf Stream, 
the slope of the bottom would become steeper, and therefore, the 
limiting depth would be attained at a shorter distance from shore, the 
consecutive reefs would be formed nearer and nearer to one another, 
and the intervening ship channels would become narrower. 



Fig. 5 is an ideal section, showing the succession of changes which would occur on 
such a supposition. The letters represent the same things as in figs. 2, 3 and 4. 

Inspection of fig. 1 shows that this has actually been the case, at least 
for the last three reefs. 

We have chosen to trace this process only so far as the northern shore 
of the everglades, because thus far we have the most indisputable evi- 
dence of the recency of the formation. But in the same manner we 
might carry it still farther back in time and northward in space, and 
represent the successive reefs by which the superficial portion of the 
rest of the peninsula was formed. 

There is one other fact of great importance, and otherwise inexplicable, 
which receives a ready explanation upon this theory, and which, I 



11 

think, therefore, is strongly confirmatory of its truth. I allude to the 
fact that the successive reefs are found at some distance from one 
another; in other words, that the peninsulars formed by a succession 
of barrier reefs, instead of a continuous southward growth of fringing 
reef. The reefs of Florida are, in some respects, entirely peculiar. 
Barrier reefs have heretofore been considered ' as always the result of 
subsidences of the sea bottom, and are invariably looked on as the sign 
of such subsidence. But in Florida, we have barrier reefs where it is 
certain there has been no subsidence. We have here, therefore, a new 
form of barrier reef. This important fact did not, I am sure, escape 
the attention of Professor Agassiz, for my own attention was first 
drawn to it by him ; but I have seen no publication in which he has 
alluded to the fact, nor as far as I know, has he ever attempted or even 
thought of a probable explanation. The explanation which I would 
offer, is as follows : 

It is a well known condition of coral growth, that the sea water must 
be pure and transparent. Corals will not grow, therefore, on muddy 
shores, or in water upon the bottom of which sediment is deposited. 
Now, it must be borne in mind, that while the Gulf Stream bears sedi- 
ment in its deeper stata, it is superficially transparent, and we have 
already shown that this must, of necessity, be the ease with ocean 
streams. Suppose, then, that the matter held in suspension by the 
waters of the Gulf of Mexico, be of such a degree of fineness, that it 
sinks to the depth of sixty feet by the time it reaches the point of 
Florida. It is evident that the sea bottom within the curve, cannot 
rise by deposit above this level, for all the sediment is below. A stream 
bearing sediment in all its strata from bottom to top — such as a river, 
for instance — will make land within the curve, but an ocean stream will 
only make shoal water within the curve. In the case supposed, where 
the bottom of the shoal rises to within sixty feet of the surface, it will 
cease to receive deposit, and the water will remain perfectly transpa- 
rent. Here, then, it would seem, we have the conditions necessary 
for coral growth. It must be recollected, however, that upon sloping 
shores, with mud bottom, such as we have supposed always existed at 
the point of Florida, a fringing reef cannot possibly form, for the water 
is rendered turbid by the chafing of waves against the mud bottom ; 
but at some distance from shore, that is, where the depth of sixty or 
seventy feet is attained, and where the bottom is uuaffected by the 
waves, the conditions favorable for coral growth would be found. Here, 
therefore, would be formed a barrier reef, limited on one side by the 
muddiness, and on the other by the depth of water. 

It is evident, then, that the Peninsula and Keys of Florida have 
been the result of the combined action of at least three agencies. First, 
the Gulf Stream laid the foundation ; upon this, corals built up to the 
water level ; and finally, the work was completed by the waves. Fig. 
4 illustrates the relative importance of these agencies. All below the 
line n n' n" n'", even to the bottom of the Gulf Stream, is due to the 
agency of that stream ; all befe* the line n n' n" n'" and the line 1 1 to 
the agency of corals, and above the line 11 to waves. 



12 

I have said that a stream running through still water, and making a 
curve, would deposit most of its sediment on the inner side of the 
curve. This is certainly true; but it is a more general expression of 
the truth, to say that a stream running through still water will deposit 
sediment on both sides, just where it comes in contact with the still 
water, and is retarded by it. It would do so for the same reason that 
rivers which habitually overflow their banks fj&fei natural levees on 
either side where the rapid current- of the river comes in contact with 
the comparatively still water of the river swamp. It is well known 
that the natural levees of the Mississippi continue out to sea in the 
form of submarine banks, evidently formed by the checking of the 
velocity of the current on either side, by contact with the still water of 
the Gulf. If the current is straight, the deposit on both sides will be 
equal, and thus the stream will form banks for itself. If the stream is 
curved, the deposit will be mostly on the inner side of the curve, as 
already said. It/is not probable that the Bahama banks, or at least that 
portion of them that lie to the east of Florida, may have been formed 
to a great extent in the same way ? That while the peninsula of 
Florida has been made on one side, the Bahama banks have been made 
on the other? It will be observed that the great Bahama banks lie off 
the eastern coast of Florida, and that the Gulf Stream runs in a narrow 
channel between them. At the point of Florida the deposit would, of 
course, be on the inner side of the curve, and would go, therefore., 
mostly or entirely to the extension of that peninsula : but after the 
stream turns northward and becomes nearly straight, the deposit would 
be also on the other side, and thus probably have originated these 
banks. Even if we suppose, as is most probable, that there originally 
existed in this position islands or submarine hills, which turned the 
stream around the point of Florida, these have doubtless been greatly 
modified and extended by sedimentary deposit. Probably, also, even 
the general form of the Atlantic bottom — very sloping until the Gulf 
Stream is reached, and then plunging rapidly into an almost unfathom- 
able abyss, forming a deep bed for thaCstream — may, to some extent at 
least, be accounted for in a similar manner, for certain it is, that a 
stream running through still water, no les < than one running over laud, 
will make its own bed; only in the latter case, by abrasion, it cuts out 
its own channel, while in the former, by deposit, it builds its own 
banks. 

This property of ocean streams, viz : that they form banks or ridges 
where they come in contact with still water, affords a possible, and, as 
it seems to me, even a probable explanation of certain remarkable pe- 
culiarities of sea bottom, brought to light by recent soundings across* 
the Gulf Stream. Commencing at Charleston, the bed of the ocean slopes 
at first very gently, so that at a distance of fifty miles from shore it 
attains only the depth of 20 fathoms, and then very rapidly, so that in 
25 miles more, it sinks to the depth of 700 fathoms or more. At the 
additional distance of another 25 miles, (/. c. 100 miles from shore,) at 

*Proc. Am. Assoc, Washington Meeting, p. 140. 



13 

the depth of 300 fathoms, is found a ridge rising from unfathomable 
depths on one (coast) side, and 1,500 feet above the hollow on the 
other side. At the distance of a little more than twenty miles more is 
found another ridge 500 feet high, followed by still another hollow. 
Further observation shows that the Gulf Stream is divided into longi- 
tudinal bauds or streams of warm and cold water, see fig. 1, and that the 
warm bands correspond to the feg*t9gi, and the cold bauds to the ridges. 

Now, these ridges and hollows may be conceived to have been formed 
in either of two ways, viz. : by igneous or current agency. As upon 
land valleys are formed either by igneous or aqueous agency, i. e., may 
be valleys of elevation or valleys of erosion ; so also in the sea, ridges 
may be formed by igneous or current agency, i. c, may be ridges of 
elevation or ridges of deposit. In either case, there would be conformity 
between the direction of the ridges and the direction of the current, 
only in the one case the current would conform to the ridges, and in the 
other the ridges would conform to the current. 

In order to account for these ridges by this current theory, the only 
supposition which it is necessary to make is, that there exists in the bed 
of the Gulf Stream, somewhere to the southward of the Charleston 
section, i. c, at the southern extremity of the ridges, two or more sub- 
marine peaks or mountains- — possibly a spur of the Bahama chain. If 
two such peaks existed in this position, and rose so high as to part the 
lower strata of the Gulf Stream, there would evidently be formed bands 
of comparatively still water to the northward, and as evidently there 
would be liues of deposit determined by the still water, and the neces- 
sary result would be the ridges discovered by the ('oast Survey. We 
see the same thing on a small scale in river currents. Every obstacle 
which parts the current determines the position of a sand ridge on the 
lower side of the obstacle, and in the direction of the current. There 
is this remarkable difference, however, between river and ocean currents 
— that while in the case of rivers the parted current quickly closes 
again, and the resulting ridge is therefore very short, in ocean currents, 
such as the < j-ulf Stream, the space between the two parts would be 
quickly filled by the cold water of the ocean. The parted current would 
have, therefore, no disposition to coalesce, but would continue as bands 
of warm Gulf water separated by bands of cooler and stiller Atlantic 
water, and the resulting ridges would therefore continue for great dis- 
tances. I know not whether there have been any observations to test 
the comparative velocity of the warm and cool bands, but it seems to me 
that on any couceivable theory, as to the formation of .the ridges, the 
velocity of the cool bands would be less. 

Now, though it may be impossible in the present condition of science 
to determine with absolute certainty whether these ridges were formed 
previous to the existence of the Gulf Stream, by igneous agency, or 
whether they have been formed since by the sediment carried by the 
stream itself, yet, when we recollect that all the other peculiarities of 
the Gulf Stream and the contiguous sea bottom are mainly referable to 
sedimentary deposit ; when We reflect how simple and natural is the only 
supposition required, and how easily it explains all the phenomena, 



14 

particularly the cold bands, which seem inexplicable on any other theory, 
unless we suppose the existence of lateral currents, it seems to me that 
the weight of probability will strongly incline to sedimentary deposit as 
the cause also of these ridges. In fact, everything about the Gulf Stream 
seems to point to the conclusion that it has been the architect of its own 
curves, its own banks and its own configuration of sea bottom. 

There is one other conclusion which, though not connected with any 
particular' theory of the formation of Florida, is, nevertheless, naturally 
suggested by the subject of this paper. We have seen that the peninsula 
of Florida has been progressively advancing towards Cuba as a fixed 
point, and the Gulf Stream has been becoming more and more narrow. 
If, therefore, as is probable, the quantity of water carried by the Gulf 
Stream has remained constant, it follows that the velocity with which 
the stream emerges from the Straits cf Florida, and therefore the dis- 
tance to which it penetrates the still water of the Atlantic, has been 
progressively increasing. Now, unless there has been some very re- 
markable change in the direction of this current, it necessarily, follows, 
that its warming influence upon the European continent has also been 
progressively increasing. Have we not here, if not a suflicient cause, 
at least one of the true causes of that preat change which we know has 
taken place in the climate of Europe since the glacial period? 

Thus we see that the advancing point of Florida has been progressively 
warming the climate, of Europe, and thus, perhaps, controlling the 
destinies of the human race. Can we conceive a more beautiful instance 
than this of that sympathy which exists between the most distant por- 
tions of our globe, and which binds all its members together in one 
organic whole? 



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